Voltage reference networks



Sept. 27, 1955 5. LE BRADLEY ET AL 2,719,261

VOLTAGE REFERENCE NETWORKS Filed Sept. 2'7, 1952 2 Sheets-Sheet 1 Fig.|.

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VOLTAGE REFERENCE NETWORKS 2 Sheets-Sheet 2 Filed Sept. 27, 1952 Fig.4.

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L r M Y U h C S United States Patent VOLTAGE REFERENCE NETWORKS Schuyler Le Roy Bradley and Powell 0. Echo, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 27, 1952, Serial No. 311,892

4 Claims. (Cl. 323-65) This invention relates to impedance type voltage reference networks and more particularly to such voltage reference networks in which the impedance characteristic can be easily modified.

Impedance type voltage reference networks heretofore have, for instance, utilized components having either a non-linear electrical characteristic and a linear electrical characteristic or two non-linear electrical characteristics to provide an intersecting point as depicted by two characteristic curves. However, these prior art networks are sensitive to frequency and temperature changes and thus tend to hold a different reference voltage or intersecting point when the input frequency or temperature changes. Also the impedance characteristic of these prior art static reference networks cannot be readily changed by an electrical signal and such changes have to be made by means of a mechanical adjustment.

An object of this invention is to provide in a voltage reference network for electrically controlling the inductive characteristic of one of the impedance circuits of the reference network by applying a low energy direct current control signal to the impedance circuit.

Another object of this invention is to provide for controlling the manner in which the input voltage to one of two impedance circuits of a voltage reference network varies with its output current as depicted by a non-linear characteristic curve representing one of the two intersecting characteristic curves for the voltage reference network, by applying a low energy direct current control signal to a magnetic device comprising the non-linear impedance circuit to thereby control the impedance of the non-linear impedance circuit and thus the positioning of the non-linear characteristic curve with respect to the other intersecting characteristic curve.

A further object of this invention is to provide in a voltage reference network means for compensating for frequency changes in the input voltage to the reference network over a wide range by providing a magnetic device as the non-linear component of the reference network and varying the magnetic saturation of the magnetic device in a predetermined manner in accordance with the frequency of the input voltage to the reference network.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawings in which:

Figure 1 is a schematic diagram of a voltage reference network illustrating an embodiment of the teachings of this invention;

Fig. 2 is a graph illustrating the linear and non-linear characteristic curves for the voltage reference networks illustrated in Figs. 1 and 4 and more particularly the different positioning of the non-linear characteristic curve for different frequencies in the input voltage to the voltage reference network illustrated in Fig. 4;

Fig. 3 is a graph illustrating the different positioning of the non-linear characteristic curve of the voltage reference networks of Figs. 1 and 4 for different directions in the current flow through the control winding of the magnetic device comprising a component of the reference networks illustrated in Figs. 1 and 4;

Fig. 4 is a schematic diagram illustrating another embodiment of the teachings of this invention, and

Fig. 5 is a graph illustrating the manner in which the output current from the frequency sensitive circuit illustrated in Fig. 4 varies with changes in the frequency of of the input voltage thereto.

Referring to Fig. 1 of the drawings, there is illustrated a static voltage reference network comprising a nonlinear impedance circuit 10 and a linear impedance circuit 12. In order to obtain a measure of the difference of the output currents of the non-linear impedance circuit 10 and the linear impedance circuit 12, a run-around circuit 14 is responsive to the output currents of these two impedance circuits 10 and 12.

In this instance the linear impedance circuit 12 comprises a capacitor 16, however, it is to be understood that other components (not shown) such as resistors could be utilized in place of the capacitor 16. When utilizing the capacitor 16, the output current from the linear impedance circuit 12 varies with the input voltage to the linear impedance circuit 12 as illustrated by curve 18 shown in Figs. 2 and 3, it being understood that the input voltage is applied to terminals 20 and 20'.

In order to render the run-around circuit 14 responsive to the output current of the linear impedance circuit 12, the impedance circuit 12 is electrically connected to the input terminals of a full-wave dry-type rectifier 22 of the run-around circuit 14 through an isolating transformer 24, the purpose of which is well known in the art.

In order to combine the output currents of the impedance circuits It and 12 and obtain a measure of their difference, a series circuit is connected to one of the output terminals of each of the rectifiers 22 and 28 of the run-around circuit 14. This series circuit comprises re actors 30 and 32 for filtering the current flow there- 'through. The other output terminals of the rectifiers 22 and 28 are electrically connected together by means of a resistor 34 having a center tap 36 which constitutes one of the output terminals of the static voltage refer-- ence network, the resistor 34 being provided in order to insure that the output voltages of the rectifiers 22 and 28 remain positive for a predetermined change in the voltage across the terminals 20 and 20. The other output terminal 38 of the voltage reference network is connected to the junction point of the smoothing reactors 30 and 32 of the run-around circuit 14. Thus, a measure of the difference of the output currents from the impedance circuits 10 and 12 can be obtained at the output terminals 36 and 38.

Although a run-around circuit 14 has been illustrated, it is to be understood that other types of circuits may be used in place of the run-around circuit 14 provided they are capable of obtaining a measure of the difference of the output currents of the impedance circuits It) and 12.

Referring to Figs. 2 and 3, there is illustrated a nonlinear characteristic curve 40 which illustrates the manner in which the alternating output current from the nonlinear impedance circuit 10 varies with changes in its alternating input voltage as impressed across the terminals 20 and 20. As can be seen from Figs. 2 and 3, the linear characteristic curve 18 intersects the non-linear characteristic curve 40 at the point 42.

In accordance with the teachings of this invention, the positioning of the non-linear characteristic curve 40 can be changed in order to compensate for ambient temperature changes and machine temperature changes, in order to introduce reactive droop or line drop compensation, or in order to provide a minimum excitation limit. The repositioning of the non-linear characteristic curve 40 is accomplished by changing the magnitude of a low energy 3 direct current signal which is supplied to a magnetic device 50. As illustrated, the magnetic device is a self-saturating reactor.

In this instance the self-saturating reactor 50 comprises magnetic core members 52 and 54 which have disposed in inductive relationship therewith reactor windings 56 and 58, respectively. As illustrated, a self-saturating rectifier 69 is connected in series circuit relation with the reactor winding 56 and a self-saturating rectifier 62 is connected in series circuit relation with the reactor winding 58 in order to insure that current flows in only one direction through the reactor windings 56 and 58, respectively. The series circuit comprising the reactor winding 56 and the rectifier 60 and the series circuit comprising the reactor winding 58 and the rectifier 62 are connected in parallel circuit relation, one end of the parallel circuit being connected to the terminal 29 and the other end of the parallel circuit being connected to one of the input terminals of the rectifier 28 of the runaround circuit 14. As illustrated, the rectifiers 60 and 62 are connected in the circuit so as to be oppositely poled.

For the purpose of varying the magnetic saturation of the core members 52 and 54 and for thus obtaining the desired compensation hereinbefore mentioned, a plurality of control windings 66, 68, 70, 72 and 74 are disposed in inductive relation with the magnetic core member 52 and a plurality of control windings 76, 73, 80, 82 and 84 are disposed in inductive relationship with the magnetic core member 54.

As hereinbefore mentioned, various types of compensation can be obtained by varying the magnitude of the input current to the control windings 66, 68, 70, 72, 74, 76, 78, 80, S2 and 84. For instance, the control windings 66 and 76 can be considered as the control windings for providing reactive compensation. As illustrated, the control windings 66 and 76 are connected in series circuit relation and the input voltage to these control windings is of the polarity shown in Fig. 1, which input voltage is received from a circuit (not shown) which produces an output signal which is a measure of the reactive power for which compensation is desired. When the input voltage to the control windings 66 and 76 is of the polarity shown, current will flow through the control windings 66 and 76 so as to produce a flux in the core members 52 and 54 which is additive to that flux produced in the core members 52 and 54 by the current flow through the reactor windings 56 and 58, respectively, to thereby increase the magnetic saturation of the core members 52 and 54. An increase in the magnetic saturation of the core members 52 and 54 increases the output current from the self-saturating reactor 50 for a given input voltage to the non-linear impedance circuit 10 and as depicted in Fig. 3, lowers the non-linear characteristic curve 40 to a lower position as illustrated by a non-linear characteristic curve 90. Thus, by increasing the magnetic saturation of the core members 52 and 54 and thereby lowering the characteristic curve 40 to a position as illustrated by the characteristic curve 90, the desired reactive compensation is obtained.

In order to provide machine temperature compensation, the control windings 68 and 78 are connected in series circuit relation and have applied thereto an input voltage of the polarity shown. Since the polarity of the input voltage to the control windings 68 and 78 is the same as the polarity of the input voltage to the control windings 66 and 76, the non-linear characteristic curve 40, as depicted in Fig. 3, is likewise lowered to such a position as represented by the characteristic curve 90 by increasing the magnetic saturation of the core members 52 and 54 to thereby provide the desired machine temperature compensation. In like manner, in order to provide ambient temperature compensation, the control windings and 80 are connected in series circuit relation and have applied thereto an input voltage of the polarity illustrated in Fig. 1. Under this latter condition the characteristic curve 40 is also lowered to such a position as represented by the characteristic curve by increasing the magnetic saturation of the core members 52 and 54 to thereby compensate for ambient temperature changes.

For the purpose of compensating for line drop, the control windings 72 and 82 are connected in series circuit relation and they have an input voltage of the polarity illustrated. However, in the case of the control windings 72 and 82 current flows through these control windings in such a direction as to produce a fiux in the magnetic core members 52 and 54, respectively, that opposes the flux produced by the current flow through the reactor windings 56 and 58, respectively, to thereby decrease the magnetic saturation of the core members 52 and 54. Therefore, as illustrated in Fig. 3, the non-linear characteristic curve 40 is raised to such a position as illustrated by a non-linear characteristic curve 91 to thereby provide the necessary line drop compensation. In like manner, the control windings 74 and 84 are connected in series circuit relation for the purpose of providing the desired minimum excitation compensation and as illustrated, the polarity of the input voltage to the control windings 74 and 84 is the same as that polarity provided for the control windings 72 and 82. Thus, the characteristic curve 40 is likewise raised to such a position as illustrated by the characteristic curve 91 in order to provide the desired minimum excitation compensation.

It is to be understood that one or more sets of control windings, such as the control windings 66 and 76 can be provided depending upon how many types of compensation are needed or desired. Thus, only the control windings 66 and 76 may appear on the magnetic core members 52 and 54, respectively, or all of the above enumerated control windings may appear upon their respective magnetic core members.

It is also to be understood that the circuits (not shown) that are connected to the inputs of the various sets of control windings 66-76, 68-78, 7080, 72-82, and 7484 produce at their output a voltage that is a measure of the particular thing for which compensation is desired, for instance, a measure of the line drop.

Referring to Fig. 4, there is illustrated a voltage reference network in which like components of Figs. 1 and 4 have been given the same reference characters. However, in Fig. 4, means are provided for compensating for changes in the frequency of the input voltage to the reference network over a wide range and thus for changes in the frequency of the voltage appearing across the terminals 20 and 20. If no means were provided for compensating for an increase in the frequency above the normal frequency of the input voltage appearing across the terminals 20 and 20, the magnetic saturation of the core members 52 and 54 would decrease and the non-linear characteristic curve 40 as illustrated in Fig. 2 would rise to a position as illustrated by a non-linear characteristic curve 92. Again assuming that no compensating means were provided, if the frequency of the input voltage decreases to a predetermined value below the normal frequency of the input voltage across the terminals 20 and 20', the magnetic saturation of the core members 52 and 54 would increase and the non-linear characteristic curve 40 would reposition itself at a lower location as illustrated by a non-linear characteristic curve 94.

In order to compensate for the above-mentioned changes in the frequency of the input voltage impressed across the terminals 20 and 20, control windings 96 and 98 are disposed in inductive relation with the magnetic core members 52 and 54, respectively. In this instance, the control windings 96 and 98 are so disposed on the magnetic core members 52 and 54, respectively, that current flow through the control windings 96 and 98 produces a flux in the magnetic core members 52 and 54, respectively, that is additive to the flux produced in the core members 52 and 54, respectively, by the current flow through the reactor windings 56 and 58, respectively.

The current flow through the control windings 96 and 98 varies in a predetermined manner in accordance with the magnitude and frequency of the voltage impressed across the terminals 20 and 20', this effect being secured by means of a frequency-responsive circuit 100 whose output is electrically connected to the control windings.

96 and 98 and whose input, as represented by the termi nals 101 and 101, is responsive to the magnitude of the frequency of the voltage appearing across the terminals 20 and 20'. In particular, the frequency-responsive circuit 100 produces an output current which varies in a predetermined manner in accordance with the frequency of the input voltage appearing across the terminals 20 and 21, as illustrated by a curve 102 shown in Fig. 5. Thus, when there is an increase in the frequency of the voltage across the terminals 20 and 20' above the normal value which tends to decrease the saturation of the core members 52 and 54 and thus the output from the non-linear impedance circuit 10, the output from the frequency sensitive circuit 100 increases to increase the magnetic saturation of the core members 52 and 54 and thereby compensate for the increase in the frequency of the voltage across the terminals 20 and 20. Likewise, when there is a decrease in the frequency of the voltage across the terminals 20 and 20 below the normal value which tends to increase the magnetic saturation of the core members 52 and 54 and thus the output of the non-linear impedance circuit 10, the output of the frequency sensitive circuit decreases to thereby decrease the magnetic saturation of the core members 52 and 54 and thus compensate for the decrease in the frequency of the voltage across the terminals 20 and 20.

The shape of the curve 102 is determined by the electrical characteristics of the components establishing a twin T filter 103 which in turn comprises variable resistor components 104, 106, 108 and capacitor components 110, 112 and 114. The shape and in particular, the slope of the curve 102 can be changed by means of a variable resistor 116.

In order to provide for magnitude adjustment of the control current flowing through the control windings 96 and 98 of the self-saturating reactor 50, a multiple tap transformer 119, having an input electrically connected to the input terminals 101 and 101 and an output electrically connected to the input of the filter 103, is provided. For the purpose of rectifying the output current of the filter 103, the output of the filter is electrically connected to the input terminals of a full-wave dry-type rectifier 120. The output terminals of the rectifier 120 in turn are electrically connected to the series-connected control windings 96 and 98 in order that current will flow through these control windings in accordance with the output current of the frequency sensitive circuit 100 as illustrated by curve 102 shown in Fig. 5.

As illustrated, a reactor 124 is disposed in the circuit that connects one of the output terminals of the rectifier 120 to one end of the control winding 96, the reactor 124 being provided in order to render the source impedance relatively high to the even harmonic frequencies induced in the control windings 96 and 98 by the alternating current in the reactor windings 56 and 58, respectively. Also as illustrated, a half-wave rectifier 126 is connected across the series circuit comprising the control windings 96 and 98 in order to obtain a self-saturating effect from the even harmonics in the control windings 96 and 98.

It is to be noted that variations in the magnitude of the input voltage to the frequency sensitive circuit 100 do not afiect the accuracy of the voltage reference network but rather increase its sensitivity. The reason being that an increase in voltage at the terminals 101 and 101' increases the current flowing in the control windings 96 and 98 in a direction to increase the saturation of the core members 52 and 54. As hereinbefore mentioned, the non-linear characteristic curve 40 is thus lowered and the current that flows through the non-linear impedance circuit 10 to the rectifier 28 increases for a given voltage input at the input terminals 20 and 20'. Thus there is a greater current difference between the current flowing to the rectifier 28 and the current flowing to the rectifier 22 than if no frequency compensating means were provided. The current output at the output terminals 36 and 38 in a direction to lower regulated voltage therefore increases for a given change in voltage at the input terminals 20 and 20'. On the other hand a decrease in voltage at the terminals 101 and 101 effects an increase in the output current from the voltage reference network in a direction to raise the regulated voltage.

It is to be understood that although no frequency compensation is provided in the voltage reference network illustrated in Fig. 1, frequency compensation similar to that illustrated in Fig. 4 can be provided when desired.

Since certain changes may be made in the above apparatus and circuits, and different embodiments of the invention may be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. In a voltage reference network, the combination comprising, two impedance circuits disposed to be supplied by a source of voltage whereby their output current varies in a predetermined manner with changes in magnitude of said source of voltage as depicted by two intersecting characteristic curves at least one of which is nonlinear, one of said two impedance circuits comprising a magnetic device whose output current varies with its input voltage as depicted by the non-linear characteristic curve, control means including a frequency-responsive circuit responsive to said source of voltage and connected to the magnetic device, the output current of the frequency-responsive circuit varying in a predetermined manner with changes in the frequency of said source of voltage to thereby vary the magnetic saturation of the magnetic device and thus compensate for changes in the output of said one of the two impedance circuits due to changes in the frequency of said source of voltage, and circuit means responsive to the output of the two impedance circuits for producing a measure of the difference of the outputs of the two impedance circuits.

2. In a voltage reference network, the combination comprising, two impedance circuits disposed to be supplied by a source of voltage whereby their output current varies in a predetermined manner with changes in magnitude of said source of voltage as depicted by two intersecting characteristic curves at least one of which is nonlinear, one of said two impedance circuits comprising a magnetic device having a magnetic core member, a series circuit comprising a rectifier and a reactor winding which is disposed in inductive relationship with the magnetic core member, said series circuit being connected to receive energy from said source of voltage, and a control winding disposed in inductive relation with the magnetic core member, control means including a frequency responsive circuit responsive to said source of voltage and connected to the control winding, the output current of the frequency responsive circuit varying in a predetermined manner with changes in the frequency of said source of voltage to thereby vary the magnetic saturation of the magnetic core member to thereby change the position of the non-linear characteristic curve and thus compensate for changes in the output of said one of the tWo impedance circuits due to changes in the frequency of said source of voltage, and circuit means responsive to the current flow through the reactor winding of said one of the two impedance circuits and to the output of the other of said two impedance circuits for producing a measure of the difiference of the outputs of the two impedance circuits.

3. In a voltage reference network, the combination comprising, two impedance circuits disposed to be supplied by a source of voltage whereby their output current varies in a predetermined manner with changes in magnitude of said source of voltage as depicted by two intersecting characteristic curves at least one of which is nonlinear, one of the two impedance circuits comprising a magnetic device having magnetic core means, two series circuits connected in parallel circuit relation, each series circuit comprising a reactor winding and a rectifier, the parallel connected series circuits being connected to receive energy from said source of voltage, and a control winding disposed in inductive relationship with the magnetic core means so that a change in the current flow through the control winding effects a change in the magnetic saturation of the magnetic core means to thereby change the positioning of the non-linear characteristic curve with respect to the other of said two intersecting curves, and circuit means responsive to the current flow through the reactor windings of said one of the two impedance circuits and to the output of the other of said two impedance circuits for producing a measure of the difference of the outputs of the two impedance circuits.

4. In a voltage reference network, the combination comprising, two impedance circuits disposed to be supplied by a source of voltage whereby their output current varies in a predetermined manner with changes in magnitude of said source of voltage as depicted by two intersecting characteristic curves at least one of which is nonlinear, one of the two impedance circuits comprising a magnetic device having magnetic core means, two series circuits connected in parallel circuit relation, each series circuit comprising a reactor winding and a rectifier, the parallel connecter series circuits being connected to re ceive energy from said source of voltage, and a control winding disposed in inductive relationship with the magnetic core means, control means including a frequency responsive circuit responsive to said source of voltage and connected to the control winding, the output current of the frequency responsive circuit varying in a predetermined manner with changes in the frequency of said source of voltage to thereby vary the magnetic saturation of the magnetic core means to thereby change the position of the non-linear characteristic curve and thus compensate for changes in the output of said one of the two impedance circuits due to changes in the frequency of said source of voltage, and circuit means responsive to the current flow through the reactor windings of said one of the two impedance circuits and to the output of the other of said two impedance circuits for producing a measure of the difference of the outputs of the two impedance circuits.

References Cited in the tile of this patent UNITED STATES PATENTS 2,428,566 Harder et al. Oct. 7, 1947 2,429,724 Krabbe Oct. 28, 1947 2,477,988 Krabbe Aug. 2, 1949 2,504,675 Forsell Apr. 18, 1950 2,509,865 Hedstrom et al. May 30, 1950 

